It is desirable in mobile communications networks for a user subscribing to a given operator to be able to change operators without the need for changing his phone number. For example, a business user would not wish to change operators if that change meant informing his customers of a new phone number, and producing new business cards, advertisements and so on showing the new phone number. Similarly, it would be inconvenient for a personal user to have to inform his friends and family of a new phone number each time he wished to change operator.
As a result of this, so-called “number portability” (NP) is now a basic feature of mobile communications systems. This allows a user to subscribe to a new network, but maintain the number allocated in the original network. For network operators to be able to switch a phone number from an originating subscription network to a new (recipient) subscription network it is necessary for certain information to be transmitted from the originating subscription network to the recipient subscription network.
In both 2G and 3G systems, an operator identifier must be changed in order to correctly identify the recipient subscription network. In 2G systems, prefixes such as 040 or 050 are used as operator identifiers to identify particular operators. An individual subscription to a network is requested by the operator identifier, e.g. 040, followed by a unique number. In 3G networks, the operator identifier is instead a postfix, such as @sonera.fi or @radiolinja.fi. An individual subscription for a network is represented by, e.g., john.doe@sonera.fi. In any number portability operation, the prefix or the postfix must be translated from the originating subscription network to the recipient network.
In all-IP (internet protocol) networks (such as 3G networks) number portability is soon to be standardised. The basic operation proposed is similar to that used in GSM (2G) systems.
In summary, a number portability (NP) database is queried during a session initiation phase. A mobile number portability database (MNP-DB) query determines if a subscriber has a new address, i.e. has been “ported out”. Depending on the scenario, this query is performed using the Serving Call State Control Function (S-CSCF) or the Interrogating Call State Control Function (I-CSCF). The MNP-DB query may be performed in the originating network (direct routing) or the recipient network (indirect routing). The NP is done by using MNP-DB query (to find out if the subscriber is ported e.g. has new address) in S- or I-CSCF depending on the selected scenario.
In 2G networks, it is possible for network operators to charge users for the NP service. The 2G solution for charging of NP requires a mobile switching centre (MSC) to generate the relevant charging data. An indication that porting has taken place is inserted into the appropriate charging data records (CDRs) by the MSC.
General charging operations in 3G networks have now been standardised. Two separate charging architectures may be used: off-line and on-line. Off-line charging provides a charging process where charging information does not affect, in real time, the service rendered, whereas on-line charging provides a charging process where charging information can affect, in real time, the service rendered, and it can therefore directly interact with the session or service control.
The postpaid and prepaid charging methods known from 2G networks also apply in 3G networks. Postpaid requires a user to pay for network usage after it has taken place, usually by way of a monthly bill. Prepaid requires a user to pay for a service before it is actually used. Money is paid to a prepaid account, and is subsequently deducted from that account according to service usage.
3G charging can be effected by means of the Diameter protocol, an AAA (authentication, authorisation and accounting) protocol defined by the IETF. This is a session-based protocol and is extensible such that it is applicable to all supported services, and application-specific functionality can also be provided through an extension mechanism. All data delivered by Diameter is in the form of attribute value pairs (AVPs). AVPs are used by the base protocol to support features such as transporting of user authentication information, transporting of service specific authorisation information, and exchanging resource usage information which may be used for accounting purposes.
In both postpaid and prepaid charging systems, accounting data is transmitted between a network element within a user's subscription network and an accounting server. Accounting requests (ACRs) are sent from the network element to the accounting server, and corresponding accounting answers (ACAs) are sent back from the accounting server to the network element.
In postpaid charging situations these ACRs and ACAs are transmitted once a service request has been allowed, throughout a communication session. After the session has terminated, a final ACR/ACA pair is exchanged between the network element and the accounting server such that the session can be billed to the user.
In the prepaid situation an ACR is sent from a network element to an accounting server following a user's request for a service. The accounting server then checks whether the user has sufficient funds for the service requested, and responds with an ACA to the network element. If the service requested by the user is then accepted, ACRs and ACAs are transmitted throughout the session and money is periodically deducted from the prepaid account. On termination of the session, a final ACR is transmitted from the network element to the accounting server instructing the accounting server to terminate the deduction from the user's account. Finally, the accounting server responds to the network element with an ACA.
To date, no proposals have been made for how number portability could be monitored, or charged, in an all-IP network. It is therefore desirable to provide a solution which is suitable for monitoring number portability in 3G networks.